If We Leap Through Time
by Tankyu-sha
Summary: War does not stop for one person, nor do fractured timestreams cease to flow. After the Battle of Alaska, in which Watase Aoba and Yumihara Hina fell back through the time tunnel, war continued; now, Dio stands in the remains of a decades-wrecked lab, and finds the final truth of the Coupling System...
1. Chapter 1: Legacy

_**If We Leap Through Time**_

* * *

 **Chapter 1: Legacy**

* * *

March, 2093, Pacific Ocean

* * *

War, Junyou Dio Weinberg had long since learned, was relentless. And humanity had all too much of a taste for it, no matter how much the saner representatives of the species tried to put the brakes to it. All it took was one madman with a grudge to set it all off again.

That was why _Cygnus_ was here, on this small island a few kilometers off mainland Japan. What should have ended five years before, in the aftermath of the Battle of Alaska, kept grinding on; the Confederacy still maintained a slim technological advantage, but East Zogilia had the most important resources of the splintered nation, along with sheer, bloody-minded determination.

 _Not to mention Evgeny Kedar's willingness to use WMDs,_ Dio thought acidly, descending Bradyon NX's zipline. The Valiancer knelt beside the grounded _Cygnus,_ a couple hundred meters from the weathered building that was the reason for their presence. _First the Gorgon five years ago, and its little brothers since, now a Nectoribium_ bomb. _What drives that bastard?_

At least that last one, he'd managed to stop. While Fromm Vantarhei and his new partner Mishima kept the other Zogilians off his back, Dio had managed to take down the Hraesvelger carrying the enormous bomb before it could reach Yokohama. Bradyon was an aging machine, and Dio could no longer use the Coupling System, but he was still good enough when it counted.

 _I never thought Alfried Gallant would be as useful an ally as he was a deadly enemy._ Picking his way through the brush and lingering bits of broken pavement, Dio shook his head. Commander Gallant and Captain—then Special Officer—O'Keefe hadn't managed to end the war with their coup after Alaska, but even after Kedar launched his counter-coup and took East Zogilia back on the offensive, they'd kept the treaty as best they could.

Overuse of Nectoribium weapons had prompted the coup in the first place. When Gallant learned of the Hraesvelger project, he'd warned the Confederacy at once, and even deployed some of his forces to help.

 _It won't be the last time Kedar tries something like that, though. That's why we need to find something to break the stalemate, and end the damn war._

Dio didn't want to be here, knowing what the wrecked lab supposedly contained. He'd stayed as far away from the subject as he could, these last five years, despite his own Valiancer still mounting the technology. But when _Cygnus_ had been called in, he hadn't even made a token protest. No one had ever laid official blame on him for what he'd done at Alaska, but he knew what was said behind his back.

He didn't even disagree, deep down. He still felt it had been the honorable thing to do, but Dio Weinberg had always suspected the war would've ended years ago if Watase Aoba had been around to fight it. And Dio had been the one to shove the naive but gifted pilot down the time tunnel, back to his own time.

Many people had died in the five years of war that had passed since. Dio felt every one of them.

Resolutely, Dio stepped over another patch of cracked, overgrown pavement, and walked into the Coupling Test Laboratory.

* * *

"I still wonder what Headquarters thinks we're going to find here," Dio heard as he made his way down a battered hallway. "Even if any of the computers are still intact, surely Professor Fermi found everything of use years ago, from the mainland lab."

"We didn't even know this facility existed until recently," a deeper voice pointed out. "Obviously _some_ things were left out of the Tokyo branch's database."

"Maybe so, but it still can't possibly have anything to contribute that we haven't worked out ourselves in the last ten years!"

"Maybe. But as we've cause to know, the past can still hold surprises for us, Doctor Conrad."

Dio emerged into what seemed to be the main computer room of the CTL to find several other members of _Cygnus'_ crew already there. Chief Petty Officer Nasu Mayuka was poking at an obsolete terminal, trying to see if she could boot it up at all, with help from Fromm's longtime girlfriend Anessa Rossetti. Behind them, Doctor Elvira Conrad was arguing with Captain Kuramitsu Gengo, while Commander Lene Kleinbeck looked on with her usual air of resigned exasperation.

 _Five years, and it's still the same crew. Aoba wouldn't have any trouble fitting right back in, if he showed up again today._

"Elvira has a point," Dio remarked, stepped over a broken chair. With a scowl, he took in the old computer room, and shook his head; the place was open to the sky in a few spots, with plants growing in odd corners. "This facility had bombs dropped on it in World War III, and who knows when it was abandoned in the first place."

"Progress was set back by at least twenty years in that war, Dio," the captain reminded him. "Professor Fermi and the Doctor here perfected the Coupling System, but the basic research dates back much farther. Unless and until we can get into the computers here, we won't know just how far the project got before it was mysteriously shut down."

"Mysteriously?"

Elvira sighed. "I don't know how much you've ever bothered to look into it, Dio, but the truth is we still don't know much about the original experiments. We have the basic conceptual model and the original Emphatier waveform baseline, but not much else. All indications are that the project was abandoned before practical tests were ever made; we don't even know who the original researchers were. The Captain's right about that much." She looked mulish; an expression Dio remembered well from whenever he and Aoba did the impossible. "But I still can't believe there's anything to be found here that we haven't worked out for ourselves!"

Typical Elvira Conrad. Even marriage to _Cygnus'_ Valiancer team commander hadn't done anything to mellow her irritation when the universe showed her something that violated her theories.

 _Not that I'm inclined to disagree this time. Aoba's the only one I ever knew who really_ could _make the impossible possible. I realize Headquarters wants a magic bullet, but this place is nothing but a wreck._

A wreck that was bringing up painful memories, at that. Dio admitted to some interest in the mystery, but if there was nothing useful to be gained here, he'd just as soon leave.

"Ah! It looks like we might just find out. Elvira-san, this terminal is still functional!"

Elvira's attention whipped over to Mayuka and Anessa. "Can you get it running, Mayuka?"

"Just a second," she said, voice muffled by the machinery she was buried in. "Let's see… Anessa, hit that right there, and we'll put it on the big screen!"

A few moments of clanking, a couple of sparks, and one uncharacteristic curse later, and all eyes turned to the biggest monitor in the room as it came to life for the first time in decades. The assembled misfits of the _Cygnus_ waited with baited breath—and Dio gasped in shock.

 _No,_ he thought, seeing the faces that appeared on the monitor. _No, that can't be!_

" _Hey, there,"_ the cheerful, brown-haired young man on the screen said with a grin. _"Maybe it's wishful thinking, but… Long time no see, siscon bastard."_

* * *

25/12/2014, Tokyo

* * *

Something in Watase Aoba resisted the idea of waking up. He was warm, a primal part of his brain insisted, and he wouldn't be if he moved. Which he'd have to, if he actually went and woke up all the way. As long as he was asleep, he could pretend it was still night, and cuddle.

 _Cuddle?_ The part of his brain that was voting for waking up realized there was something odd about that, and dragged the rest of his cerebrum kicking and screaming toward the light.

It still took him a few minutes, but gradually Aoba became aware of the world outside his own head again. The first thing he realized was that, judging from the air on his face, his hind brain had been right: once he got out of bed, he'd be freezing.

The next thing to come to his attention was that it wasn't even his bed. This realization/recollection was followed very swiftly by the recognition that his hands were tangled in hair, and that he was so warm because that hair belonged to a girl currently sprawled across him, legs entangled with his own.

Right. Aoba remembered now. Staying the night at Hina's new apartment, having to share a bed because of the building's furnace being out of whack—and Hina's kiss and confession. Followed by his stammered response, and more kissing—Ryutaro, he thought with a flush, might've called it "making out"—before they'd finally curled up to sleep.

 _I guess I'm the first one awake,_ he thought, blushing but content in Hina's arms. _Still can't quite believe last night really happened…_ But he was in Hina's bed, she was sprawled across his chest, and it was her hair and the skin of her back that his hands began to stroke.

Aoba smiled when his actions drew a sleepy sound of contentment from Hina, the more so when she moved to burrow her head deeper under his chin. This, right here, made everything he'd gone through in his sojourn to a future war worth every minute. _Hina,_ he thought, still running his hand up and down her smooth back. _I came so close to never knowing just what life could be with you. If time hadn't twisted just right…_

It took a few minutes, especially as he had no particular interest in moving, before he realized something was off. The way her chest moved against his body as she sleepily responded to him was a pretty big clue, though, and with a start, he figured out what was wrong.

 _Eh? Skin? …Uh-oh._

Aoba couldn't see past the blankets, but he knew he shouldn't have been feeling skin under his fingers. That meant either his hands had gone somewhere they _really_ shouldn't have, or something had happened with Hina's yukata. Given just how distinctly he was feeling her breasts on his chest, he could guess which it was.

 _I'm dead._

Before he could even begin to think of a way to extricate himself from the wardrobe malfunction he was accidentally taking advantage of, Hina began to stir. "Mmm… Aoba?" she murmured, eyes fluttering open. Turning her head to look up at him, she smiled sleepily. "Good morning, Aoba…"

"Ah, g-good morning, Hina," Aoba replied nervously, trying to discretely move his hands away from her back.

She noticed both his movement and his anxiety, and tilted her head in confusion. "What's wrong, Aoba?" Hina shifted, pushing herself up to get a better look at his face—and in the moment the blankets shifted enough to let the morning air in, she froze.

 _Help?_ Aoba thought, watching as realization chased sleep out of Hina's expression. She had, fortunately for his peace of mind, stopped before he could see more than her bare shoulders and a bit below her collarbone, but he was sure that was more than enough to earn him at least a slap. From the way her face rapidly reddened, he judged there was an excellent chance he was about to be kicked out of the bed entirely.

One possibility that, somehow, didn't occur to him at all was that an embarrassed smile might appear on her face, followed by her wrapping her arms around his neck and pulling herself close for a searing kiss.

Conscious thought fled Aoba completely for awhile, lost in the feeling of Hina's lips on his, her tongue slipping into his mouth, their bodies pressed so tightly together that only his thin shirt separated his chest from hers. Somehow, in the middle of it, his hands had returned to her back, holding her against him; from the intensity of the kiss, she didn't seem to mind.

When she did finally pull back, the both of them panting for breath, Hina quickly dragged her yukata closed, but didn't lose her smile. "We're a couple now, right, Aoba?" she said shyly, face still bright red. "A boyfriend can get away with a little… indiscretion now and then. Don't you think?"

"Um. Yeah," Aoba managed, brain still rebooting. "Er. That was…"

"Mm. Yeah." Hina leaned into him again, slipping far enough back under the covers to rest her head on his chest. "…I guess you should probably get going soon, Aoba. But… can you stay, just a little longer?"

Like he was going to say no, after _that?_ "Of course, Hina-chan," he said, reaching up to stroke her hair again. "…I love you."

Those words were still hard for Aoba to force out past his embarrassment, but the way Hina cuddled closer in response made it all worthwhile. _This has got to be the best morning of my life,_ he thought, gently kissing the top of her head. _And to think, this time last year I never even knew Hina existed. Heck, I don't know for sure if she_ did _exist then._

That, he decided not to dwell on. After everything that happened since the day Bizon Gerafil appeared out of nowhere to shoot up his school, Aoba had learned a lot about temporal mechanics, none of which managed to form a coherent picture of how any of it actually worked. All it did was give him a headache.

 _I hope things went okay with the_ Cygnus, _though. I'd never complain about Dio's last "gift", but I know it must've left a hole in their combat power. …Hell of a risk, siscon bastard. I hope it didn't cost as much as it gained us._

* * *

March, 2093

* * *

Mayuka had paused the recording and whipped out of the shell of broken machinery to gawk as soon as the first few words were uttered, giving all the assembled crew a moment to just stare.

Three figures in lab coats. One they all knew well, for all that it had been a few short weeks, and he was clearly older by at least as many years as had passed for them. Another they had a couple of recorded images of, and knew more from reputation; the third, Dio had seen in a handful of memories. None of them would they have _dreamed_ of seeing in this context.

"Aoba?" Elvira said numbly. "Dio… that's Aoba, right? Our Aoba?"

"…Yes," Dio breathed. "That's him, all right." He recognized the nickname, if nothing else, and for once was too stunned to take offense. "Which means that must be Yumihara Hina next to him."

"Aoba-san," Mayuka whispered, eyes shimmering. "He made it back…"

The relief in her voice was palpable, and brought a twinge of guilt to Dio. The girl had never said a word to him in reproach, but he knew it had hurt her when Aoba never came back. All she ever said was that she hoped he'd made it safely back to his family.

Since then, Mayuka had almost never said Aoba's name at all.

"The plot thickens," Kuramitsu murmured. "Start it up again, Chief. Let's see what secrets Aoba left for us."

"Ah! Y-yes, sir!" Mayuka darted back to resume the playback, then hurriedly returned to Dio's side to watch it herself.

" _I know I'm taking a chance that it's you guys seeing this,"_ Aoba's image said, grinning. _"But I figure sooner or later, it'll get to_ Cygnus. _I'm sure you're still at the cutting edge of Coupling development. Well, if the war's still going on, anyway… but I've got a feeling it is."_ He sobered. _"It's hard to say for sure what holds true for this particular timeline, but—well. I'll get to that in a moment."_

Calm. Thoughtful. And right on the nose with his predictions. This might still be Watase Aoba, but it was obviously an Aoba who'd had a few years to grow up since Dio knew him. But then, he'd have had to, to be in the role this message implied he was.

" _The first thing I want to say is, thanks, Dio."_ Aoba grinned again, obviously imagining the look that would prompt. _"I know. Surprising, right? But seriously, Dio. I know what it must've cost you, and the_ Cygnus, _to send us back, but from a personal standpoint, it was the best gift you could've given us. We've lived the lives we're 'supposed to', as you said that day, and it's been grand."_

" _He's right, Dio,"_ Hina agreed, stepping closer to the camera. _"I never knew you in th_ _is_ _timeline, but… thank you. For that, and for everything before."_

 _Before?_ Dio wondered. _"Th_ _is_ _timeline"? What does she mean?_

" _I'm sure you've got a lot of questions, Dio, everyone,"_ Aoba said, taking up the narrative again. _"Let me start by saying that if you're blaming yourself for sending away an important combat asset, don't. What you did was more important than you knew; it wasn't just good for our personal lives…"_

* * *

March, 2017

* * *

In time, the daily reality of high school began to push memories of war from the forefront of their minds. Even for Hina, who had lived a far more "complete" life in the future, the present gradually became "normal", helped by the bits and pieces of memory she was starting to recover that hinted at more than just her endless loops.

Helped, even more, by her new-found relationship with Aoba. In every loop, Hina had been driven by the need to protect him from the attack she always knew was coming; yet also, in the months she watched over him from afar, she'd always felt a stronger pull toward him than just a debt. An attraction, she could admit to herself now, that she'd never had time to act on.

Now she did, and the time since she returned from the future had been the happiest in her life. It saddened Hina to think that, to know that Victor Ryazan would never have understood her choices or the truth of her existence, but it was a fact. And whether her adopted father could've understood or not, Aoba did. He understood—and loved her.

There was, as far as Hina was concerned, no greater Christmas present than the discovery that he felt the same way she did. And as embarrassing as the morning had been, she didn't regret one second of it. Except, maybe, not _quite_ having the courage to take things farther still, but she supposed neither of them was quite ready for that.

Yet, anyway.

For now, Hina's primary regret was that they couldn't hide their relationship forever. Ryutaro was sworn to silence, but it was inevitable that Aoba's other friend, Junichi, would figure it out before long, and from there it was all over the school. Not that she was at all ashamed of it, or even really _wanted_ to hide it—it just made it more difficult to get Aoba alone, they way they had been for that one night.

Still, whether they could manage to sleep in each other's arms the way she really wanted to on a regular basis, there were more than enough opportunities to steal the odd kiss, away from prying eyes, and share meals, and even go on genuine dates. Like the normal high school students Hina had never been able to be before, and Aoba had almost lost the chance to be.

At the least, it was fun to watch even Ryutaro and Junichi give them odd looks, when they laughed at being called a "couple". And, however it may have felt at the time, even high school didn't last forever.

"Man," Aoba said around a yawn and a stretch, "I can't believe it's gonna be over soon. That felt like forever!"

"I've sometimes thought exams were worse than combat, the last couple years," Hina agreed with a smile. The two of them had just left school, the very last day of regular classes finally over. "And that was just the regular high school tests."

"Ugh. Don't even remind me about the college entrance exams." Aoba shivered. "If I hadn't remembered more of what I learned on the _Cygnus_ than I thought… Talk about a nightmare." Between what he _did_ manage to remember of Mayuka's lessons, and some intensive study sessions with Hina, he'd managed to scrape through not only the last high school finals, but even the entrance exams for their chosen college. He'd even gotten decent marks on both.

That hadn't made either one any more fun. Hina was right: at least in combat, you could _shoot_ your problems and have done with it. School wasn't nearly so straightforward—especially not school on the career track they'd both finally settled on.

 _It's funny, though,_ Aoba mused, casually taking Hina's hand as they headed for the train station. _It's been years, and it was only weeks to begin with, but sometimes it still feels like just yesterday that I was flying Luxon and making Elvira-san tear her hair out with Dio._

He hadn't been in Luxon NX's cockpit since moving it out to sea, but sometimes, in his dreams, Aoba found the Valiancer's controls in his hands again, fighting against Zogilia like he had for those short weeks that, to the rest of the world, still hadn't even happened yet.

"War leaves an impression, Aoba," Hina reminded him, easily following his thoughts from his expression. Squeezing his hand, she continued, "I understand it's not as bad for pilots like us as it is for soldiers on the ground, but it still makes its mark." She favored him with another smile. "It helps to have someone to talk to about it, though, don't you think?"

"It sure does." Fortunately, not only was Hina firmly living in the same timeframe as he was now, half the time she was in a position to sneak into his room for a few hours of the night. The problems with central heating that had led to their first night sharing a bed had turned out to be foreshadowing a comedy of errors.

By now, Aoba thought, Hina had spent at least fifty percent of the last two and a half years living in the Watase household, with her chronic bad luck with apartments. They thought she might, finally, have found a decent one this time, but she hadn't yet had a chance to move in. So tonight she was, again, coming home with him.

Neither of them, he thought, really minded. They'd never gone farther than literally sleeping together, and even that rarely and only when Hina had her own apartment, but those few hours a night they managed when she was living with his family were still worth it—the more so now that they were officially together.

"All that's left now is graduation," Hina mused, now that they were arriving at the station. "Then… the real hard part starts, I guess."

"Yeah. But we know we can do it."

It wouldn't be easy, Aoba was sure, the work that they were going to begin. But they knew it _could_ be done, and after two years of thinking about it, they had a pretty good idea of their part in things. It was, after all, the only way certain facts made any real sense.

"Still, even college is still a few months away," she said, shaking off the more serious thoughts. "Say, Aoba… I should be moving into the new place the day before graduation. Could you come over after the ceremony? We can have our own little housewarming party." For some reason, she blushed then. "And I… have a graduation present for you."

On the one hand, that made Aoba inclined toward sudden panic, as he hadn't thought of a present to give her yet. On the other… "Of course, Hina," he said with a warm smile. "Where else would I go?"

Yet again, he thought that Hina's smile was worth everything he'd gone through, from that September morning through all the battles in the future. It was cliché, maybe even sappy—but there was nothing in the world he valued more.

* * *

March, 2093

* * *

" _That's right, Dio,"_ Aoba's image said, bowing with a flourish. _"Doctors Watase Aoba and Hina, specialists in quantum physics and lead researchers on the Coupling System Project."_ He grinned. _"Never figured me for a science guy, did you, siscon bastard? Me either, really, till Hina and I started comparing notes. You know what they say, on_ _c_ _e is an accident, twice is coincidence, three times is enemy action? Well, we weren't quite on three, but two was pushing it, when it was so exact. You know what I'm talking about, right, Elvira-san?"_

He couldn't possibly have known for sure who would be present when his message was finally played, but Aoba paused anyway for effect, looking—by sheer coincidence—very close to where Elvira really was standing. The physicist hadn't _quite_ collapsed into one of the few chairs in the room that still seemed intact, but she was rubbing her temples as if to soothe a headache.

"Of course," she said, sounding half-awed, half-exasperated. "Aoba's Emphatier waveform perfectly matched the baseline we based all our experiments on to begin with. And while we never got a good reading on Yumihara, she was obviously an even closer match than Dio, given what happened when they Coupled. I always _thought_ it was a ridiculous coincidence."

"But it wasn't a coincidence at all," Kuramitsu said, nodding. "Aoba matched the baseline because he _created_ the baseline, tuned to his own brainwaves." He chuckled ruefully. "I don't really want to think about the temporal physics involved, though."

 _Ugh,_ Dio agreed silently. _He invented it because he realized he'd invented it. Aoba, you still manage to make my head hurt, even when you're not even here._

Mayuka, he noticed, didn't seem to be paying much attention to that detail. Probably, he thought sadly, she was focused on Aoba's implicit reference to "Watase Hina".

 _I do wonder how the other girl got involved, though. If I remember what I saw of Aoba's memories right, she seemed even less likely a scientist than he was._

" _That's right,"_ Aoba continued at length, nodding. _"When Hina and I realized we both matched the baseline, we figured there was only one way that could be. One way or the other, as test subjects or researchers, we were involved in the original experiments. And yes, we did think of the ontological paradox._ _The answer to that one is as complicated as everything else. And believe me, this whole thing is_ very _complicated in places_ _…"_

* * *

March, 2017

* * *

It was all over now, even the fanfare. The Aoba and Hina that now walked away from the train station toward her apartment were no longer high school students: with the end of the graduation ceremony, they were officially free of it, and off to the next stage of their lives.

"It's hard to believe it's finally over," Hina mused, slipping her hand into Aoba's with none of the blushing hesitation that had marked the first days of their relationship. "All those loops, and I never quite made it to graduation. The closest I ever had was graduating the abbreviated officer training in Zogilia. Somehow, that just didn't have the same impact this does."

Aoba gave her a thoughtful look. "How much do you remember of the earlier loops, anyway? I know you said when we got back that you remembered at least a little of 'this' timeline…"

"Bits and pieces have come back to me over the years," she said, looking pensive. "It's hard to say how much, because the details were mostly the same from one loop to the next. I know some things were different, though; like the loop you caught a glimpse of, just before you followed me into the time tunnel."

A version of events wherein Dio had prevented him from going after her, something which had only changed because this last time, they'd succeeded in Coupling with Skyknight and Firebrand, giving Dio a glimpse of his own into Aoba's past. Aoba only had a few fragments of memory himself of that timeline, but thinking about it still gave him the chills.

Even now, they had no idea just how long Hina had been repeating the same stretch of time. Given the nature of temporal phenomena, it could easily have been thousands of years or more of repeated time, until the one time something had changed.

 _Maybe there were tiny changes each time, that gradually added up to one big one?_ Aoba wondered, unconsciously squeezing Hina's hand. _The one thing that stopped this timeline from going like all the ones before was Dio seeing my memories when we used the prototypes. Why did it work this time, and not before? …Ah, this makes my head hurt._

"It doesn't really matter what happened before, Aoba," Hina reminded him, giving him a gentle smile. "We're finally moving forward, after all this time. Let's worry about today for a while, not the past or the future."

"Yeah. You're right."

For the rest of the walk to Hina's new apartment, they kept the topics light, just simple, cheerful smalltalk. Whatever had happened before, the endless loop was finally broken; whatever would happen in the future, could _wait_ for the future. Today they'd finally left the Purgatory of high school behind, and were determined to celebrate the fact.

Hina's new apartment was different from those she'd tried before, and was actually located in the warehouse district where she'd once kept her Karura. Finally fed up with the series of lemons she'd lived in for such brief periods, she'd asked in exasperation of the owner of the very building she'd once rented storage space in if he had any ideas. The result was an apartment above just such a warehouse, its somewhat inconvenient location compensated for by the low rent and better-than-average privacy.

As they ascended the outside staircase leading to the unorthodox apartment, Aoba couldn't help but chuckle. "Well, at least you probably don't have many problems with door-to-door salesman," he said, shaking his head. "Does the climate control at least work right?"

Hina smiled. "Most of the building is food storage. It smells a bit strange sometimes, but it's always the right temperature. Not that my first apartment, after we got back, was _all_ bad, ne?"

Aoba flushed, but he wasn't about to disagree. If they hadn't ended up sharing a bed for warmth, who knew how long it would've taken for one or the other of them to confess? _Well,_ he thought, while she unlocked the door, _maybe not_ that _long. Though it might've spared us some embarrassment._

He blushed even brighter at that memory. He hadn't _quite_ seen Hina topless, but he'd come close. Certainly he'd _felt_ a lot more than he was comfortable with—and she hadn't exactly seemed to mind…

Aoba chopped that thought off in a hurry, and followed Hina into the apartment. Couple or not, they were here to celebrate her new lodgings and graduation from high school, not for him to get any perverted ideas. _Focus, Aoba,_ he told himself. _Focus on… Hm. Smells kind of like cheese in here. What_ are _they storing down there right now?_

"The smell is a small price to pay," Hina said, seeing his expression. "Everything works, the rent's cheap, and we're not likely to be disturbed. Besides, there's worse smells than cheddar, right?"

While she busied herself locking the door and turning on the lights, Aoba nodded ruefully. "Point. A lot better than some of what I dealt with on _Cygnus."_ He shuddered. "Some of what Saburouta-san had me clean up when I was 'initiated' into the crew… Ugh."

She giggled. "Yeah, I can imagine. There are some things I saw—and smelled—that I don't really want to remember, either." Hina went to the small kitchen area, rummaged about for a few moments, and emerged with a cake. "Enough about that. I invited you over to celebrate, right?"

"Right."

They took to the task of eating cake with enthusiasm, both of them hungry after the long graduation proceedings, and followed up with a little more substantial fare for a proper meal. It reminded Aoba of a certain Christmas Eve, actually, though today was much more comfortable, both physically and emotionally.

He was _not_ going to think of Tsubasa's coy suggestion, that very morning, that she and their mother "wouldn't wait up" for him, this one time.

At length, when they'd finished eating, both stood from the table, Aoba unsure of what to do next. Hina seemed to have some idea, though, so he watched her quietly, ready to follow her lead.

"You know," she said quietly, turning to face the window behind her, and the sky that was beginning to darken, "it's kind of funny." Hina brought her hands to her chest, though Aoba couldn't see from his angle what exactly she was doing. "I've probably put on this uniform thousands of times, hundreds of thousands, over all the years I was looping. Now, tonight, will be the very last time I ever take it off."

Aoba tried to banish the images _that_ turn of phrase immediately brought to mind, but a moment later Hina made the attempt pointless. Cloth shifted as she turned, and when she was facing him once more it was with her shirt unbuttoned, hanging loosely from her shoulders.

He hadn't had the slightest idea, before that moment, that she hadn't worn a bra that day.

Aoba choked. "H-Hina—!" he blurted, flushing, stammering, but somehow unable to look away. "W-what are you—?"

Blushing brightly herself, Hina was nonetheless smiling when she shifted her shoulders, letting her shirt fall to the floor. Making no attempt to cover her breasts, she reached down, unzipped the side of her skirt, and let that drop, as well, followed quickly by the flimsy cloth beneath.

Naked now save for her socks, Hina shyly put her hands behind her back, just incidentally pushing her chest forward in the process. She was blushing at least as much as Aoba, but she still managed a giggle at the look on his face. "I did say I had a present for you," she said.

Um. Well. Yes, yes she had, but it had never remotely entered Aoba's head that she could possibly mean what she was hinting at now. Actually, he thought as he struggled to come up with some coherent to say, surely she didn't _actually_ mean it that way. She was probably just giving him a bit of a show, not—

Hina cut off his thought processes completely by stepping forward and pulling him into a burning kiss. Lips moving against his, tongue forcing its way into his mouth, Aoba didn't even realize she was using her hands as well. Only when she wrapped her arms around his neck, deepening the kiss, did he realize from feel of her bare breasts on his chest that she'd undone his shirt, as well.

Untold moments of instinctive action later, including his hands doing things and going places he was dead sure would've gotten him slapped once upon a time, Aoba returned to something resembling sensibility to find his shirt had disappeared entirely in the interim, his belt was likewise AWOL, and he was groping Hina's breast while she made a good try at dealing with his pants in between moans and more kissing.

She seemed to come back to herself at about the same time he did, and though she made no move to remove his hand from her chest—instead reaching up to hold it in place—she did let go of his waistband. "Aoba," she said, breathless, "my bedroom. Please."

Aoba wasn't about to argue with that. Dense he may have been, but when his girlfriend stripped, drew him into that kind of intense make-out session, and asked him to take her to bed—

He picked her up, kissed her again, and carried her to the bedroom. And never did, somehow, make it home that night.

* * *

March, 2093

* * *

" _Of course, it wasn't as simple as that,"_ Aoba noted, hands tucked casually into his labcoat pockets. _"We had the goal figured out by the end of high school, but we still needed to work out the steps to reach it. Neither of us had any particular scientific grounding, and, well, I'm afraid most of what you told me was a bit over my head, Elvira-san."_

"Why am I not surprised?" Elvira muttered, putting a hand to her forehead. "Half of what you pulled you did because you didn't know it was impossible to begin with."

Dio nodded absently. It had driven him nuts, the way Aoba would always say something like, "You never know until you try." What made it even more irritating was how often the naive time traveler had been _right,_ against all sense and laws of physics.

" _We did, at least, have_ some _basic education from your time,"_ Aoba's image was continuing. _"Hina grew up there, and I did get something out of your lectures, Mayuka-chan."_ Mayuka made a sound that might've been a choked-off sob; if his expression was any indication, Aoba had predicted that, too. _"Really, I appreciated everything you did to help me get up to speed… Anyway, between that and the few things I picked up from Coupling with Dio, getting into the right university wasn't_ too _hard._

" _Long story short, Hina and I got through education a bit ahead of schedule, and then got down to business working out the theory behind the Coupling system. By the way, Elvira-san, you figure out a_ lot _of interesting possibilities when you happen to know time travel is possible on more than just the elementary particle level."_

Elvira paused in the middle of shaking her head again. "Time travel… Wait, could that mean…?"

"Doctor?"

She resumed her interrupted action, more quickly, at Kuramitsu's inquiry. "Later, Captain. I just realized I never thought through the implications of what that singularity proved was possible… Actually, Aoba's probably about to explain it, anyway." Elvira still looked chagrined, but for the first time she was starting to look genuinely intrigued, as well.

Dio was starting to feel that way himself. _What did you discover, Aoba? What_ were _you doing, that got this lab shut down?_

" _Now, like I said, it does help to know things are possible to begin with, and with the results we were producing Hina and I got the funding we needed to start scaling up pretty quickly. From the establishment of our dedicated lab, it took less than a year to work out the basic theory."_ Now Aoba took one hand from his pocket to scratch the back of his head, looking sheepish. _"Which, of course, is when we ran into problems. We expected our first activation of the test model Coupling System to be a low-grade version of the link we'd managed with Luxon NX and Karura. It, ah… didn't work out that way."_

* * *

June, 2022

* * *

Aoba bent over the control console, giving the settings a final check. "Baseline is set," he murmured, "power settings look about right… Both units are connected to the main computer and to each other. All that we should need now is to push a few buttons, and we're set."

The intern assisting him gave him an annoyed look. "Honestly, Aoba, I've got it. Really. Maybe I've never seen it in action, but I have been here the whole time you've been putting it together." She huffed irritably. "If you're that worried, why didn't you just build off the units you've already got?"

"The technology is a little too advanced yet for us to match it," Hina told her. She was already lying on one of the test beds, just waiting for her husband to finish the final checks and get into place himself. "Besides, we've got enough of an ontological paradox here as it is. Once we've got the first equipment and test data complete, maybe then we can experiment a little without risking further paradox."

"If you say so." The intern shook her head. "If you two hadn't shown me those robots, I'd think you were _completely_ crazy, but… Aoba, hurry up and lie down. Let's get this started."

Aoba ruffled her hair with a laugh, annoying her further, and moved to sit. "All right, all right. I admit it, I want to see how well this works, too." Swinging his legs up onto the test bed, he reflected that this was probably going to have one of the least unexpected outcomes of any "first" experiment in scientific history. He already knew firsthand what _should_ happen, after all.

 _It's been too long since we did this,_ he thought, settling into place. _I haven't Coupled with Hina since the day we got thrown back here._ _This won't be as good a link, but it's a start._

"Ready, Hina?" he asked.

"Ready," Hina replied. "Go ahead, Tsubasa-chan."

"Here goes nothing," Aoba's little sister muttered. "Okay, here we go. Coupling in three… two… one… Now!"

There was a _thrum_ as circuits powered up, something Aoba didn't remember from the Coupling Valiancers he'd flown but was unavoidable with the power-intensive prototype he and Hina had put together. Just for this brief Coupling, they'd use up at least a week's worth of the building's usual electricity budget.

The audible hum was followed by one in his mind, and for a split second he _felt_ Hina, a distant shadow of the link they'd once shared through their Valiancers. Just one moment of sensing her mind reaching out to his—

Then there was a blinding flash from the other test bed, and Hina's presence vanished from his mind with a painful snap.

Crying out, Aoba shot upright on the bed, just as Tsubasa shouted in alarm. "System overload! Emergency shutdown—Hina-san!"

He whirled to face the other test bed, but it was too late. Nothing remained there, save the smell of ozone and faint scorch marks on the sheet. Hina had disappeared.

* * *

March, 2093

* * *

" _Hina disappearing into thin air wasn't exactly what we had in mind,"_ Aoba said with deliberate understatement, still looking sheepish. _"After everything we went through to break her out of that endless loop… If I'd had any idea something like that even_ could _happen, I might've thought twice about trying to be the ones to create the Coupling System."_

"Obviously it worked out, though," Kuramitsu mused, as if speaking to the long-vanished Aoba. "If Yumihara was there when you recorded this message…"

" _As you can see,"_ the image continued, preempting him, _"it did work out in the end. And boy, did it explain a_ lot _of things that had had us stumped."_

* * *

June, 2022

* * *

Later, Aoba might've had the presence of mind to compliment his sister on her cool thinking under pressure. He could hear her rapidly tapping keys and muttering status checks to herself as she went over everything the system had recorded in the brief few seconds of the experiment.

Later, maybe. Just then, he only had eyes for the empty bed that should've held his wife, and for reasons he couldn't understand suddenly didn't. "Hina…" he whispered, horrified. "No. No, this can't be happening… Why…?"

"There was a power surge for point-seven-five seconds," Tsubasa muttered behind him. "Tripped every breaker on campus, put _everything_ into the Coupling System—how on _earth_ didn't it blow up from the overload? All that power had to go _somewhere!"_

Later, he might worry about that. Might try to figure out what and why. Right now—

"What the hell—System overload! It's reactivating itself!"

The lights dimmed, then went out entirely—but in that moment the room was bright anyway, a golden flash filling the entire lab. When it faded, the air was smelling even more of ozone, but the test bed was no longer empty.

It'd been eight years since he'd seen that flight suit, Aoba reflected numbly. Zogilian-issue, it was—but more importantly, whether it was what she'd been wearing when she disappeared or not, it was _Hina._ And when she looked up at him, and smiled, his brief spell of paralysis was broken.

"Hina!" he cried, half-tackling her across the test bed. "What happened?!"

"It's okay, Aoba," she said in his ear, hugging him tightly in return. "I'm back. And… I finally understand." Hina pulled back far enough to meet Aoba's eyes, and smiled again. "We've got a lot to talk about, Aoba."

* * *

March, 2093

* * *

" _If you guys are seeing this message, then records of that little incident should still be recoverable, too."_ Aoba's image shook his head, slipping his hand back into his pocket. _"That was the close of the time loop that Hina had been trapped in for so long. More like a spiral, really; you should see the temporal chart we worked out afterward, it looks like something out of an Escher painting… But now we finally knew where it all started, and ended."_

Dio didn't think he wanted to see that chart. His head hurt just thinking about it in the abstract, without the hard data. Judging from the fact that Elvira had actually gotten out some painkiller, he suspected it was even worse for someone who had some actual education in the field.

"Einstein would've _hated_ you, Aoba," the doctor muttered, after popping a couple of pills. "Did you have any idea how many theories you were debunking…? You must've, you remembered at least some of what Mayuka taught you…"

Hina was stepping forward again. _"It's actually kind of funny, Dio. Do you know what we learned? Through the final set of loops that experiment sent me through, I saw the beginning. I caught a glimpse of the 'original' timeline, before the Coupling System changed history. The spiral began with that same experiment, in a world where Aoba and I grew up normally, and met for the first time in college. In that time, we came up with the Coupling Theory by ourselves, without knowledge from the future._

" _And in that original world, it was me that appeared in Luxon's cockpit in 2088. I was your partner through all those battles, until the Gala Puska ripped open time, and sent me back to my high school years."_ Hina looked pensive. _"We still don't know, exactly, how many times I passed through those years, but now we finally know that I was born a normal girl—and now we have the endpoint of the paradox."_

Dio blinked at that revelation. There had been a time when he'd teamed up with _Hina,_ and never known Aoba at all? That was a strange thought, to say the least.

" _We still aren't sure on one point,"_ Aoba noted, taking the lead again. _"Specifically, whether time operates on a linear, mutable line, or if the 'Many Worlds' theory is actually correct. Because of the particular timing of the leaps, we haven't been entirely certain; though we do have a few indications that it's a variant of the former. If it is, the timestream is clearly very elastic, but… Well. We've got an idea for how to prove it._

" _Whether this message is intact for you to see or not, or if any other data survived in this mainframe, we've taken steps to preserve out research. You'll find a hardened data storage room beneath the main lab facility, deep enough to avoid anything short of a direct nuclear attack, and hardened against EMP."_

Kleinbeck, heretofore silent, immediately brought up a comlink. "Kleinbeck to Chief Naher. We've just learned there should be a bunker below the main facility. Prioritize search efforts on finding it."

 _Aoba grew up after all,_ Dio reflected. _That's… more careful than I'd have expected that whiner to be._

" _We've got quite a bit of data you may find useful, Elvira-san,"_ Aoba's image was saying. _"I'm sure you've made improvements of your own since I left, but I think our team traveled down a few avenues you may have written off as blind alleys. After all, we had proof of just what the system was really capable of."_ His expression turned grave; Dio thought the only time he'd seen Aoba look _that_ serious was just before he somehow managed to convince him to go up in Skyknight and Firebrand. _"As you obviously know, we did eventually stabilize the Coupling System so that it only sent thoughts, not people, into the future. But we weren't content with that, when we knew it could do so much more._

" _One thing we know: that by the time Professor Fermi restarted the project, our original team had been lost to history. The obvious assumption is that we were killed in the war that wrecked my neighborhood—but_ _there is one other possibility. So, Dio, Elvira-san, everyone: we leave this message as we prepare for one final experiment. If it doesn't work, well, you'll find the data on it in the secure records."_ Aoba suddenly smiled again. _"If it does? Well…"_

* * *

February, 2023

* * *

He probably had done more difficult things in his life, Aoba thought, especially some of the crazier battles he'd fought flying off the _Cygnus_ years ago. Still, few of those things had been quite as _complicated_ as moving two eighteen-meter-tall robots to an island research facility without anyone—especially anyone official—being the wiser.

Between the three of them, though, they'd pulled it off, and Luxon NX and Karura now knelt on the floor of an improvised hangar off the Coupling Test Laboratory's main building. They were being inspected now by the handful of mechanics and engineers Aoba and Hina had brought in on the secret over the years.

"Damn shame we can't publish the specs," Aoba heard one of them mutter, as he himself pored over test results of the Valiancers' modifications. "Can you imagine what Japan could do with this kind of hardware?"

"You wanna cause a paradox? Even the docs are aiming for a time after they last left." The other engineer snorted. "Besides, it'd take us most of those seventy-odd years just to build the tools to make these things. We just can't _do_ it, not yet."

Aoba privately wished much the same, but after all the temporal headaches he and Hina had already had, they weren't inclined to take chances. If they did this right—probably even if it went wrong—the spiral would remain a closed loop, and they very much wanted to keep it that way.

 _So far, the data looks good,_ he thought, bringing up the next page on his tablet. _It's too bad we can't get more empirical results before we try it for real, but it's too risky._ _The small-scale unmanned test was chancy as it was._

"We'll make it, Aoba," Hina told him, coming up to rest her head against his shoulder. "We've done the impossible every other time we tried, right? This is just one more."

Aoba put an arm around her shoulders. "Yeah, you're probably right," he agreed. "Like I always told Dio, we'll never know until we try." He smiled at the memory. "And every time we did, we worked out something. Drove Elvira-san crazy, of course."

Strange. Eight and a half years on, and those few weeks on the _Cygnus_ were still vivid in Aoba's memory. Such a short time, over seventy years in his own future, had come to completely define his life, from his relationship with Hina to his career in life, completely derailing the vague ideas he'd had before that September afternoon.

He still wondered, occasionally, where he might've gone with his life if it hadn't been for that experience. If he'd lived through the timeline where he and Hina had developed the Coupling System without having spent time in the future. Would they have just continued their research as normal, even after that first botched experiment?

 _Well, we might've changed our focus some,_ Aoba decided, holding Hina close with one arm and skimming the next page of test data. _But without the personal experiences, the people I met on the_ Cygnus— _and let's not forget Fiona; I wonder how she's doing?—I doubt we'd even be considering_ this.

It was completely crazy, on the face of it. Elvira-san would've called it outright impossible. Indeed, it _would_ have been, if they'd tried this right after returning to 2014; Luxon NX and Karura simply weren't equipped for something like this. They'd only accomplished anything like it before thanks to the titanic energy release the Gala Puska had supercharged them with.

They'd learned by accident that it was possible to do it with much less, and the fruit of several months of dedicated research had been attached to the two Valiancers and was even now undergoing final inspection.

"I _still_ think you're crazy," Tsubasa groused, climbing down from the aeroscale module on Luxon's back, where some of the new equipment had been mounted. "Even with the results from the unmanned test. Trying it full-scale like this…"

"You don't have to come with, Tsubasa-chan," Hina pointed out gently. "We can do this alone."

Aoba's little sister snorted, looking away. "And then do what, huh? With Mom gone—"

Aoba nodded soberly. Their mother had died suddenly not long after Hina's accidental temporal excursion, which had left the three core members of the Coupling Development Project with few ties outside the project itself. There was, he supposed, _technically_ Hina's original family, but considering that her "past" self was growing up as normal in this time—

 _I hate temporal mechanics,_ he thought, shivering at the reminder of just how twisted the timeline had become over the many iterations of Hina's loop.

"Anyway," Tsubasa said, brushing away the somber atmosphere with a wave of her hand, "I may think you're crazy, but I admit I'm interested. All those stories you told me, the little bit we got from the drone test—how can I pass this up? It's the chance of a lifetime."

"Yeah. You're right about that." On several levels, really. On top of Aoba's personal reasons, there were the strategic implications, given the data they'd gotten from the drone, which had shaped some of their last-minute preparations. And, if he was going to be perfectly honest, his pride as a scientist—not an expression he'd ever thought he'd apply to himself—would be bolstered considerably if this worked.

 _I never thought to check back then. Do they still give out the Nobel Prize?_

"Hey, Doc!" The chief of the Project's mechanics waved a wrench in their direction. "Everything looks green here. You guys are the experts on the science stuff, but if that checks out too, you're good to go."

"Right." Aoba took a deep breath, and reluctantly took his arm from Hina's shoulders. "Let's check the Coupling System and quantum entanglement apparatus one more time, and get ready."

* * *

How many times _had_ she worn this flightsuit, Hina wondered, fastening the collar of the purple bodysuit. Just taking into account the "current" timeline, it had been quite a number; but she'd thought, eight and a half years ago, that she never would again. Not after coming back to this time period.

The accident in the first Coupling test had changed that view irrevocably, and now Hina didn't care to guess when she might really be putting it away for good.

 _The good news is,_ she thought with some amusement as she walked back into the hangar, _that "accident" meant I had two of these available. Even if my old one did have to be tailored a bit._

A couple of steps behind her, Tsubasa fiddled with the cuffs of the flightsuit Hina had been wearing when she and Aoba first returned to 2014. The fit wasn't quite perfect, even with the alterations that had been made; Tsubasa simply wasn't built the same as Hina, especially in the chest. It would be good enough, though, for what they were doing.

"Somehow," Tsubasa mused, "this makes it feel real. We really are about to do something amazing, aren't we?"

"We are," Hina agreed, smiling at the sight of Aoba coming out of the facility's other locker room. It _had_ been almost nine years since she'd seen him in that blue and white flightsuit, after all—though what _really_ made her smile was how it clearly fit little better than Tsubasa's borrowed suit.

He'd grown a fair few centimeters since he last wore it, after all. It had taken almost more work to make the old suit fit than it had to ready the Valiancers for the experiment.

"Are you two ready to go?" Aoba asked, trotting over to them, helmet under his arm.

"Ready as we can be," Hina replied, meeting him halfway and sliding easily into his arms. "Nobody has ever done anything like this."

"Yeah. We get that a lot, don't we?" He drew her into a deep kiss, no less passionate than the ones they'd shared when they first got together. Parting only when Tsubasa coughed pointedly, he grinned. "Come on. Let's go make history. Or maybe write the future?"

He and Tsubasa made for Luxon NX, while Hina headed for Karura. She'd originally become its pilot against her will, drugged and manipulated by Doctor Hahn's twisted version of the Coupling System, but that had been years ago. In the course of the experiments and modifications of the Project, she'd made the Valiancer truly her own.

 _Now to hope I haven't gotten too rusty,_ she thought, climbing into the cockpit. _…No. I'll be fine. Together with Aoba, we'll do just fine._

A few well-practiced motions brought Karura online, the cockpit that had one belonged to the original Luxon lighting up as if it had been a frontline unit only yesterday. Within seconds, the regular status readout on the main display changed, stating **COUPLING URGENT SEARCH MODE** , a message that brought another smile to her face.

" _Everything all set?"_ Aoba said over the radio.

" _Ground crew, all clear here,"_ the chief mechanic reported. _"We're all out of the predicted area of effect, Doctor. And then some."_

" _Roger that, Chief."_ Hina could hear the grin in Aoba's voice; the engineers, if anything, thought they were even crazier than Tsubasa did. _"Hina?"_

"I'm ready, Aoba."

" _So am I… I hope,"_ Tsubasa chimed in. _"If I get sick in here, I'm opening my helmet, though. Fair warning."_

" _Hopefully, it won't come to that."_ The first trace of uncertainty crept into Aoba's voice, though it was tempered by his own self-confidence. _"Okay, then… Connective, Hina!"_

"Acception," Hina replied at once, finishing an exchange they'd only had a chance to make once before.

At once, the special gear mounted around her seat shifted around, coming to life with kaleidoscopic light—light that was outshone by the sparks in Hina's mind as her consciousness reached out to, and met Aoba's. It was well beyond the link they'd managed with the prototypes they'd put together themselves, a warm, strong connection she hadn't felt in almost a decade.

She'd missed that. Oh, how Hina had missed those few, glorious moments she'd been Coupled with Aoba. And she could _feel_ that Aoba felt exactly the same way.

" _Incredible,"_ she heard Tsubasa mutter through the euphoria. _"You were right: the Valiancers' more sensitive systems_ do _register your Emphatier waveforms as if you were one person. This might just work after all."_

" _It will,"_ Aoba said, with absolute conviction. _"Better yet, our other hypothesis should be valid, too."_ He tapped a few keys on his display; Hina could sense through their connection the way he carefully examined data that would once have been meaningless numbers and graphs to him. _"Everything looks stable, Hina. Shall we start Phase Two?"_

She nodded unnecessarily; she knew he could feel her agreement perfectly well. "Let's go, Aoba. Let's leap through time again."

Aoba was grinning, Hina was certain. _"Right. Initiating feedback loop; cross-connecting to the quantum entanglement system. Increasing reactor output… Capacitor charging steadily. Singularity jump in three… two… one…"_

The world beyond Karura's cockpit went bright gold, swirled into a kaleidoscopic vortex, and vanished.

* * *

March, 2093

* * *

" _See you soon, siscon bastard…"_

 _It's dusty in here,_ Dio told himself, feeling his eyes sting. Aoba's image tossed his audience a jaunty salute, grinned, and disappeared in the wake of that final statement; and Dio was sure the dust had gotten stirred up by something, because his eyes were watering badly enough now he could hardly see.

"Aoba-san…" Mayuka was crying openly, but that wasn't surprising. She'd probably been closer to Aoba than any of them, and the sheer finality of that message…

Kleinbeck looked like she was considering reprimanding Mayuka for her lack of professionalism, but even before Kuramitsu paired a sharp look with a minute shake of his head, she had clearly discarded the idea. If Dio didn't know better, he'd have suspected even she was affected by Aoba's final message; at the least she was obviously inclined to let emotional reactions slide just now.

Instead, she turned her attention to the open channel she still had to Chief Naher, and began speaking in a low voice. At the same time, Kuramitsu turned his attention to Elvira, who had finally pulled up a reasonably intact chair and sunk into it. "So, Doctor Conrad?" he asked quietly. "Do you have any guesses about what Aoba was trying to achieve?"

Elvira sighed, rubbing her temples. "I'll know for sure if that backup database really is intact, but that could take days to even reach. I _might_ be able to make a few guesses, based on what he said, I suppose… The first point is that we can assume he had access to effectively everything we had on the Coupling System up to his disappearance."

"Even if he didn't remember, Luxon NX's database and equipment would have most of it," Mayuka whispered, looking at the floor. "It… sounds like they started building on that, once they'd independently 'invented' the basic theory."

"Right," Elvira agreed. "On top of which, Aoba _knew_ our theories about the system's limitations were flawed, and he always was more ready to take chances than we were. Like with Skyknight and Firebrand."

And at least half a dozen other incidents, Dio remembered, but that probably was the most extreme case of doing the "impossible". It had taken Elvira weeks to figure out how they'd managed a Coupling with the system specifically set to prevent it, and her answer had boiled down to "he's a perfect match, he can make it do whatever he wants".

 _Some of that was me, of course… but my Emphatier waveform altered in direct response to Aoba's. He was also the catalyst._

"Bearing that in mind," Elvira was saying now, "Aoba and Yumihara just might have come up with some theories we haven't thought up yet, after all. They _might_ even have discovered some of our recent problems, depending on how much experimentation they actually did with Luxon and the Zogilian Valiancer."

Kuramitsu nodded thoughtfully. "Then there might _be_ a 'magic bullet' here, after all."

"Maybe," she conceded reluctantly. "It all depends on how much they were able to do with Luxon, with the technology available at the time. And how much they were able to extrapolate." Another sigh, and a look that suggested the painkillers hadn't been strong enough. "Doctor Hahn was able to figure out a lot just from the basic theory and examination of the original Luxon and Bradyon cockpits, so who knows what they might have found."

She seemed skeptical still, if not as much as when they'd first arrived. Still, something in the Doctor's expression… "Doctor Conrad," Dio began, frowning. "You _do_ have some idea, don't you?"

Elvira grimaced. "From what Aoba said? Yes. It's crazy, but with Aoba that just makes it _more_ likely. There's even empirical evidence that it's _possible._ It's just…" She looked away—about as directly away from _Mayuka_ as she could, Dio noticed. "I don't think it _worked,"_ she said softly. "If it had, we—"

Whatever she might've been about to say was cut off with shocking suddenness by a siren. _"Captain!"_ came the loud, anxious voice of Lieutenant Framboise, when Kuramitsu brought up his comlink. _"_ _There are incoming radar signatures; they're confirmed to be East Zogilian!"_

"Understood," Kuramitsu replied, with the studied calm that had brought _Cygnus_ through so many battles more or less intact. "We're returning to the ship. Be ready for takeoff as soon as we arrive."

" _Prepping now, Sir!"_

The captain turned to Dio. "Dio, get back to Bradyon, and support Fromm and Mishima. We _cannot_ let this lab fall to East Zogilia."

Dio nodded sharply, and headed for the door. He still didn't know what secrets might be hidden beneath the wrecked facility, but now he at least believed there _were_ secrets to be found. Maybe even secrets that would lead to the end of this war, after all this time.

 _Aoba left something here for us,_ he thought, rushing back down the decrepit hallways. _We have to find out what it was. His legacy to us… I won't let Kedar destroy it!_

* * *

One thing about flying even a second-generation Coupling Valiancer: even without a partner to link with, it was _still_ the most advanced Valiancer of its time, and held up well enough even five years after its roll-out. Never intended for true mass-production, Bradyon NX was built to higher standards.

 _Higher than these mass-produced Zogilian models, anyway._ Dio lashed out with the blade in Bradyon's left hand, neatly bisecting an East Zogilian Krishna, then followed up with a shot from his Nectar rifle to immolate most of the torso of an Ogre. _They're still using machines from five years ago, too._

The nice thing about East Zogilia being the product of a civil war, he supposed. They simply hadn't had much of a chance to develop new hardware; which, come to think of it, probably explained their heavy emphasis on WMDs and Coupling technology.

" _No sign of Coupling Valiancers yet,"_ Mayuka reported from _Cygnus,_ mirroring his thoughts. _"I'm not reading any Emphatier_ _waveforms but ours."_

Fromm and Mishima, wreaking havoc on the vanguard of the East Zogilian force. The latter might be green, but Dio admitted he got the job done—although like with Aoba in the early days, it was still somewhat unclear how much was Mishima's own skill, and how much was borrowed from Fromm.

Regardless. They'd gotten warning early enough to intercept the Zogilian force a good five kilometers out from the island, and were still holding them at three. The problem was that the enemy formation was much larger than might've been expected—whatever they were up to, it was no mere raid.

 _They must've gotten word somehow about what's here. And they want it at least as badly as we do—or to make sure it's destroyed, if they can't have it._ Dio threw Bradyon to one side, dodging a Zogilian Nectar rifle shot, and returned fire with prejudice. _But then… why don't they have Coupling Valiancers here? If they're going to this much trouble…_

There wouldn't be a good answer to that, he was sure. It was only a question of just how bad the answer would be.

" _Hm? I'm picking up something new at the edge of the Zogilian formation,"_ Framboise reported, sounding puzzled. _"A Valiancer… I think. But it's a big one; I don't recognize the signature…"_

Something in Dio went cold. He wasn't sure what was coming, but he knew instinctively it was the answer to his question.

" _Strange,"_ Mayuka murmured. _"I'm starting to register… something… on the Emphatier_ _measurements. Elvira-san, could you take a look? It's almost like white noise, but…"_

" _Hm. You're right… I've never seen anything like this. Unless—"_ A sudden intake of breath. _"Wait, this is—!"_

A double shout of pain interrupted her, and Dio looked up just in time to see Fromm and Mishima's Valiancers fall out of Coupling mode. "What the hell—! Fromm, what's happening?!"

"I… don't know…" Fromm gasped out. "Some kind of… forced decoupling… Mishima, are you—"

He never got an answer. An enormous Nectar burst flashed across the sky, completely enveloping Mishima's Valiancer and only narrowly missing Fromm's. The green pilot never even had a chance to scream; by the time the bright orange blast had faded, his Valiancer had been atomized.

Mishima would never answer anything again—but there _was_ a voice on the radio, one whose laugh made Dio's blood run cold.

" _So, here it is,"_ the rough, aged, _gleeful_ voice said. _"After all this time, I've finally found it."_

A face appeared on Dio's monitor then, that of an old man wearing respiratory gear. With a start, he realized it was none other than Evgeny Kedar himself. _What the—what's_ he _doing here?!_

" _I know you,_ Cygnus," Kedar said, chuckling in a way Dio found strangely disturbing. _"I waited seventy years to have my revenge—only to have it stolen five years ago. Now, at last, I find_ something _of that bastard to destroy."_ The chuckle turned to a full-throated laugh. _"Destroying what he tried to protect will be a start—but here, now, I can desecrate even Watase Aoba's last legacy!"_

* * *

 **And Now, A Word From The Author**

Well, here we are: one more _Buddy Complex_ story to cap things off. I intended this to be a final one-shot to round out what I've taken to calling the _Paradox Trilogy,_ but it ended up growing beyond my expectation. Next chapter probably won't be as long, but what remains is too big to comfortably fit in this.

I realize the temporal physics is a bit… wonky, but that was kind of a given with _Unisonia_ 's setup. Fortunately, the time travel mechanics in-series are already a tad brain-bending, so what's a little more?

Mildly lackluster battle section at the end, I know. Next chapter I'll try to do better, but either way the battle is only a means to an end, not really a primary facet of the fic.

In case anyone is wondering, no, I've not given up on my _DOA/SAO_ story, and in fact have around two-thirds of the first chapter written. I merely realized I need a refresher on the series before I go much farther, and in any case _Leap_ grabbed me like the Plot Bunny of Caerbannog and wouldn't let go until I did something with it.

At any rate, I would hope this story so far lives up to _Echo_ and _Unisonia,_ and I shall endeavor not to take a year to conclude it. There yet remains a reunion, after all…


	2. Chapter 2: Closed Loop

_**If We Leap Through Time**_

* * *

 **Chapter 2: Closed Loop**

* * *

Tension aboard _Cygnus_ was thick. In one day, they'd gone from the shocking revelations of the original Coupling System Project to an assault by East Zogilia—one clearly intended to wipe out the legacy _Cygnus'_ former time-displaced comrade had left behind.

It shouldn't have been too much of a threat, with the forces the Confederacy had arrayed around the lab. East Zogilia was unquestionably dangerous, but this deep in Confederacy territory, with several teams of Coupling Valiancers, an assault should've been unthinkable.

Doctor Elvira Conrad, standing behind her protege Nasu Mayuka's station on _Cygnus_ ' bridge, was forced to confront that unthinkable notion, and the means East Zogilia had used to _make_ it thinkable.

"What's going on, Doctor Conrad?" Captain Kuramitsu asked, as calm as ever despite the situation. "What happened to our Couplers?"

"I'm not sure," she admitted unhappily, staring intently at the readouts on Mayuka's display. Outside, the standard Valiancers on both sides continued to rip and tear at each other, and somewhere much closer than she was comfortable with Dio dueled with the strange Valiancer Evgeny Kedar had appeared in. "There's some kind of interference, but I've never seen anything like this!"

"And why is Premier Kedar himself here?" Commander Kleinbeck muttered. "He said something about Watase—why should he care?"

Elvira didn't know, but she was sure Kedar's Valiancer was somehow the key to what was going on. Dio was putting up a good fight against it, exchanging Nectar rifle fire with the strange, heavyset unit, but for an ungainly machine piloted by a geriatric politician, it was performing disturbingly well.

"Look at these values, Elvira-san," Mayuka said, drawing her attention to a purely tactical section of the display. "The acceleration rate of that Valiancer… That shouldn't be possible outside of a Coupling!"

The scientist didn't know the mechanical details of Valiancers very well, but certain parameters were so closely tied to the Coupling system that she'd learned them by heart years before. Acceleration was one of them, with the physics-stretching speed of Coupling Valiancers being one of their greatest strengths.

"It's like it _is_ a Coupling Valiancer," Elvira muttered, more to herself than anyone else. "But there's still no sign of any partner, and no Coupling could be formed on _either_ side with this interference anyway! Unless he's a cyborg or some ridiculous thing like that…"

With a rumble that shook the ship, a stray blast from Kedar's immensely powerful weapons slammed into _Cygnus'_ Nectar Curtain. "Doctor Conrad," Kleinbeck called over the din, "we need a solution! If we don't get the Coupling systems back online—!"

"I'm working on it!"

Outside, Elvira could see Confederacy Valiancers going down, and the larger explosions of ships here and there. Dio was keeping Kedar mostly occupied, and Fromm was putting up a good fight despite what had to be a near-incapacitating headache, but even she could tell they were losing ground fast.

 _Think!_ she ordered herself. _One Valiancer, acting like it's Coupled with no Buddy in sight, interference preventing Coupling entirely… Doctor Hahn's up to something new, and the key has to be in there, but… Wait. The SAC theory? But we never pursued it because of the dangers! If it failed—_

"Elvira-san," Mayuka said, looking up at her, "what about the SAC theory?" Before Elvira could recover from the surprise that Mayuka was following her train of thought and provide the obvious counterpoint, the younger woman continued, "I know _we_ didn't pursue it, but Doctor Hahn wouldn't care about the danger—"

Elvira swore. "Of course he wouldn't… Captain, we may have figured out what's going on!"

"What is it, Doctor? And can you do anything about it?"

She bit her lip. "Well, a couple of years ago, our experiments suggested an alternate application of the Coupling system, what we labeled Stand Alone—"

Before Elvira could get any further, the entire ship was abruptly rocked to one side, and she was nearly thrown from her feet. At the same time, blinding yellow light erupted somewhere beyond the starboard viewports.

 _What the—I know I've seen that before!_

"Singularity detected one hundred meters to starboard!" Framboise called out. "Origin unknown!"

 _As if we ever know what causes—now what?!_ Mayuka's displays had suddenly lit up with additional telemetry, and even as Elvira stared a data stream started pouring through. Completely ignoring what should have been secure firewalls, the transmission promptly bootstrapped itself through _Cygnus_ 's systems and continued on to Bradyon NX.

"Incoming transmission, bypassing our security!" Mayuka yelped. "Source is—wait, Captain, this is—!"

" _Sorry to be so abrupt,"_ a voice said over the comm systems. _"But we're in a bit of a hurry. Elvira-san, we need to talk, fast!"_

* * *

 _What the hell is going on here?!_ Dio raged inwardly, firing off a Nectar rifle shot at Kedar, only to see it dodged with contemptuous ease. Out of the corner of his eye, he saw another Confederacy Valiancer fall to a missile barrage from one of East Zogilia's submarines, and he cursed under his breath.

He'd hated the Coupling system for years, but he had to admit that it was one of the greatest advantages that the Confederacy had. Without it—especially after having had five years to grow accustomed to relying on it—they just weren't able to hold back the East Zogilian assault.

Dio heard a cackle as Kedar fired a massive blast past him, and an explosion a moment later signified the demise of one of _Cygnus'_ sister ships, the flying battleship going up with a big enough bang to send several Valiancers tumbling out of control. By himself, Kedar was posing possibly the greatest threat on the entire battlefield, with his powerful, inexplicably mobile Valiancer.

Swearing with increasing frequency, volume, and vileness, Dio snapped off another Nectar blast and spun away, darting away from the embroiled forces. For whatever reason, Kedar seemed focused on Aoba—of all people—so if the old man happened to know that they'd once been partners, maybe…

A mocking laugh over the radio seemed to confirm the theory. _"Yes, that's right! Run, just like Watase Aoba ran back to the past! Without him, you're nothing but an insect, to be squashed at my leisure!"_

The energy blast that nearly vaporized Bradyon at least served to prove Kedar was indeed chasing him. As he threw the Valiancer into a wild corkscrew, though, Dio knew he couldn't keep it up forever. Sooner or later, Kedar would either succeed in shooting him down, or would get bored and return to the main battle. If Elvira couldn't figure out how to compensate for the interference in the Coupling systems by then—

Bright yellow light erupted into being without any warning at all. It was some distance behind Dio and his opponent—somewhere closer to _Cygnus,_ he thought—but it was enough to distract them both; when he turned to look, he saw Kedar, too, spinning around to face the source of the interruption.

 _What the hell—that's a singularity!_ Dio thought, incredulous. _Why would—_

Alarms sounded in Bradyon's cockpit. At first he thought it was related to the singularity, but when he glanced at his displays he found them in total disarray; from the look of it, something was forcibly rewriting part of Bradyon's operating system on the fly, completely ignoring the Valiancer's firewalls.

After that brief glance, Dio found himself having to fight Bradyon's controls just to stay airborne. The in-flight alterations to the OS were wreaking havoc on flight systems; if Kedar had been less distracted, he was quite sure he would've died in that moment.

" _A time tunnel?!"_ Kedar rasped incredulously. _"It can't be—you—?!"_

Dio didn't know what the old man was talking about, and didn't have time to try and figure it out. Abruptly, his displays stabilized, showing first **SOFTWARE UPDATE COMPLETE;** then, **STAND ALONE MODE READY.**

 _Stand Alone Mode? What—_

" _Dio!"_ Elvira called, sounding thoroughly shell-shocked. _"Activate the new protocol, now! Link with Bradyon!"_

He had _no_ idea what was going on anymore. It was all coming too fast, with no explanation whatsoever. Without time to even try and make sense of it, he could only act on instinct. Calling to mind a command he hadn't given in five years, he said, "Connective, Bradyon!"

It was completely unlike linking with Aoba. There was no sense of any kind of intelligence on the other side, no bleed-over of emotion or reflex; only a sudden flood of tactical information going right into his mind, and a sense of time slowing down.

Along with a sound of anguish from Evgeny Kedar, whose Valiancer jerked and bobbed in the air, momentarily out of control. The cry shook Dio out of his own immobility, and he rushed right for Kedar's Valiancer, reveling in the physics-defying speed he hadn't felt in five years. Whipping out Bradyon's sword, he slashed through Kedar's right arm in a dash that took him through and past before the Zogilian could recover.

"That's got it!" a voice called triumphantly. "We were right!"

" _It's you,"_ Kedar gasped out, his machine stabilizing, despite the sparking from its severed shoulder joint. _"You've come back… after all these years, you bastard, you're back—!"_

"Aoba…?" Dio whispered in utter disbelief. Bringing Bradyon around for another pass, he finally saw exactly what was emerging from the time tunnel: in the fading glow of the dissipating singularity, Luxon NX and Karura hovered, looking no more worn than they had five years before.

A window sprang open on his display, showing a face he hadn't seen in person in just as many years—but _had_ seen, looking just as it did now, less than an hour before, in recorded form. Barely visible behind him, a glimpse of someone else from that same video. "Yo, Dio," Watase Aoba said cheerily. "Long time no see, siscon bastard!"

"What—you— _how?!"_ Dio demanded, stumbling over his words.

" _Watase Aoba!"_ Kedar shouted, before Aoba could reply. _"Seventy years, I've thought I could never get my revenge—now, here you are, right where I can finish you!"_ Improbably, the old man laughed delightedly. _"And here I thought I was going to have to settle just for destroying your legacy!"_

"Not happening, Bizon," Aoba replied, his face suddenly assuming a deadly calm that Dio had never before seen from him. "If you thought we came here just to let you blast us—whoa!" Luxon dashed sideways, shoving Karura out of the path of a Nectar cannon blast from Kedar, and Aoba _tsked._ "Right, no time for reunions. Dio, we're about to try something kinda reckless, okay?"

Dio surprised himself by chuckling. "Like 'reckless' ever stopped you before?"

Aoba grinned. "You know it. Hina, you ready?"

"Of course, Aoba." The girl Dio only really knew from the memories he'd seen from Aoba appeared on Bradyon's display now, and said in tandem with him, "Connective, Dio!"

Dio didn't hesitate. "Acception!"

It was at least as different from his past experiences as his brief Coupling with Bradyon itself. Instead of just one mind, he felt himself connecting with two—two which operated on such a close wavelength that he could only barely tell them apart. In that instant, he could see the entire battlefield—everything in the view of Luxon, Bradyon, or Karura, the link reported to him.

If he hadn't been so experienced with the insanity that was Watase Aoba with a Coupling system, Dio would've been overwhelmed by sheer sensory overload. As it was, he gritted his teeth against the strain and held on; the initial shock passed quickly enough for him to notice the spheres of cast-off energy that erupted from their respective Valiancers, converged, and merged in the same way he'd seen five years before.

This time there was no giant Nectar cannon shooting at them, but it was still enough to provoke a garbled shout from Kedar. _"You… all these years, and you_ still _mock me, Watase Aoba!"_

Beneath his voice, Dio heard someone else yelling; someone on a dedicated link to Kedar, he supposed. _"Not possible! You… whoever you really are, you can't possibly have_ done _something like this! Not with the resources of your time! Not like this!"_

"Doctor Hahn, I presume," Aoba said dryly. He shook his head, and looked out the display at Dio. "Let's wrap this up, Dio!"

"Right." Kedar's Valiancer was missing an arm, but obviously was still combat-capable—and there were still plenty of other East Zogilian forces around. Their plan with the Coupling interference seemed to have prevented them from deploying Coupling Valiancers of their own, but that was the only handicap they really had.

If Dio was right, though, Aoba's stunning reappearance was going to make the difference.

" _Watase Aoba is mine,"_ Kedar snarled over the radio. _"Disable Hina if you must, but do_ not _kill her, either! The other boy… shoot him down!"_

Dio took that as his cue to move, turning away from Kedar to face the regular East Zogilians that rushed to obey the Premier's command. The first to reach him, the pilot of a commander's Alsiel, would probably have posed a significant threat to him just a few minutes before; now, with the power of the Coupling system backing him again, he dodged to the side of the Zogilian's cannon fire, darted forward, and sliced him in half with one smooth stroke.

A similar fate befell the team of two Ogres and a Krishna that tried following their commander's lead, and then Dio was among the vanguard.

Through the Coupling system, he could mostly follow Aoba and his partner's actions at the same time. When Kedar finally threw his bulky unit into motion again, they split to either side in a perfectly-coordinated pincer—against a team of Zogilian regulars who'd gone for _Cygnus_ while everyone else was distracted. Dio heard a yelp over the radio at the sudden motion—from Aoba's passenger, he thought—but the Zogilians were probably the more surprised.

They'd likely counted on Kedar's presence preventing Coupling operation. Even if they'd been prepared for the alternative, though, they obviously weren't prepared for Watase Aoba.

 _He hasn't lost his touch,_ Dio thought, watching with a corner of his mind as Luxon drew both of its swords and dove into the fray. A slash here, a whirling chop there; Valiancer parts went flying, and when an Alsiel turned the Nectar rifle it was carrying on him, he was suddenly somewhere else. The shot went wild, followed by the rifle and then the top half of the Alsiel when Karura blurred around behind it and tore it apart.

The unexpected tactic was both wreaking havoc on the Zogilians and leaving Kedar obviously scrambling to catch up. Forced into a chase rather than the direct clash he'd clearly expected, the old man swore bitterly. _"After seventy years, you finally reappear, Aoba—and now you won't even face me?!"_

"Some of us have better things to do than nurse old grudges, Bizon," Aoba responded calmly; he didn't even sound winded, a far cry from the excitable youth Dio remembered. "But if you really want it—come and get it!"

He and Karura whirled around together, their rifles suddenly pointed at Kedar. It was the Premier's turn to pull away sharply, his odd variant of the Coupling system allowing him to dodge Luxon's Nectar fire, yet not quick managing to avoid Karura's shell-firing weapon.

Armor-piercing rounds left deep dents even in Kedar's heavy armor as he pulled away. _"_ _I'm going to kill you, Aoba,"_ he growled. _"I will kill you, and level the entire island, along with your precious Swan! And Hina—what I'm going to do to_ you _will make you wish you'd been obedient all those years—gah!"_

Pursued by Aoba and Karura's fire, Kedar's Valiancer stuttered in the air, the bright light on its fuselage fading. For an instant, Dio wondered why—then realized that, modified though it may have been, there was one weakness to the Coupling system Kedar must still have been subject to.

" _Why is it shutting down?!"_ Kedar demanded. _"Now is not the_ time _for this!"_

Again, there was that other voice in the background. _"Even in Stand Alone Mode, there's an inherent time limit,"_ the voice said, sounding harried. _"If you go past it, the consequences—"_

" _I don't care! Aoba is finally here, and I will_ not _let him get away again!"_

" _You're out of time anyway! Look at the radar, why don't you!"_

Dio blinked, and followed the instruction himself. There were, on close inspection, a rather large number of new blips heading for the battlefield, sweeping down to engage the East Zogilians' north flank. _"Cygnus,_ " he called, "are you seeing this?"

He got an answer, but not from _Cygnus. "Attention, Confederacy forces. This is Alfried Gallant; we are coming to your assistance."_

" _Much appreciated, Commander Gallant,"_ Captain Kuramitsu replied, sounding as calm as ever despite the heavy losses of the day. _"We've already received some unexpected reinforcements, but more is always welcome."_

"… _So I see, Captain. I hope you'll be allowed to explain it, later."_

A loud, angry curse erupted from Kedar's Valiancer, obscene enough to make Dio wince. _"So,"_ he continued after, sounding very bitter. _"You live another day, Watase Aoba. You'll wish you hadn't… All East Zogilian forces, pull back!"_

" _Let them go,"_ Kuramitsu instructed, just before Dio could try and give chase. _"Protecting the lab is the top priority right now."_

"Thank you for that, Captain," Aoba said, sighing; he seemed to be watching Kedar flee with a very tired expression. "I don't know if our backups survived to the present day, but if they did, it'd be a big help; there's only so much data we could fit in the Valiancers."

" _I'm sure, Ensign—or should I say, Doctor?"_ There was a definite smile in Kuramitsu's voice. _"Would you please join us aboard? Your wife has clearance too, of course; I see no reason to be concerned about her loyalties at this point."_

"Thank you," Aoba said again. "We'll be aboard shortly." He looked back up out of Dio's display, grinning again. "Shall we, Dio? We've got a _lot_ to talk about."

Dio nodded, unable to trust himself to speak now that the crisis was past. _"A lot" is an understatement. How… how are you even_ here? _And… why?_

* * *

Déjà vu was really the only way to describe how Dio felt, setting Bradyon down in _Cygnus'_ hangar beside Luxon. Five years on, and it still felt more natural than the many solo landings he'd made since.

The illusion was quickly shattered, though. Landings five years ago hadn't included half the crew showing up in the hangar—and the Zogilian Coupling Valiancer information exchanges with Alfried Gallant had named as Karura had never been aboard _Cygnus_ at all, nor its pilot. _For that matter, Luxon NX never actually landed here, either…_

He'd spent five years wondering if he'd truly made the right choice that day. It looked like he was about to find out.

Karura's pilot was the first to come down from her cockpit. Dio twitched at the sight of her Zogilian flightsuit; intellectually, he knew that this pilot was no enemy, but old habits died hard. Even after five years of occasional joint operations with Alfried Gallant's forces, Zogilians made him uneasy. That unease faded quickly, though, when she pulled off her helmet, revealing a face that Dio remembered very well, if only through someone else's memories.

Among the assembled _Cygnus_ crew, though Kleinbeck looked about as uncomfortable as Dio had, Kuramitsu favored the young woman with a friendly smile. "So, at last we meet the mystery girl our lost pilot caused so much trouble over. Welcome aboard _Cygnus…_ Yumihara Hina, I presume?"

"Watase Hina, actually," she corrected, offering a salute. "Doctor, if you want to get technical. Captain Kuramitsu, I take it? My husband will be down shortly; things in Luxon's cockpit are a bit cramped right now."

Dio thought he heard a strangled noise of distress from the throng of crew; he couldn't see where it came from, but he was pretty sure he knew. There was only one person aboard who would react like that to someone calling Aoba their husband, after all.

He had no time to spare for Mayuka, though, as at that moment Luxon NX's hatch cracked open, admitting two figures. The first one down wore a familiar—if somewhat worse for wear—Confederacy flightsuit; the other… Dio found himself suppressing a smile, to his own surprise. The flightsuit the girl was wearing might've looked twin to Hina's in cut and style, but it clearly had needed a fair bit of work for it to fit its current owner.

"Hey, guys," the boy—no, Dio corrected himself, man; to his shock, the other pilot now looked older than _he_ was—said cheerfully, pulling off his helmet. "So… long time no see?"

"Doctor Watase, I presume." Kuramitsu shook his head. "It has been a long time, yes—longer for you than for us, I'd guess. Welcome back."

"It's good to _be_ back. Though I bet you've got a couple of million questions for us, even with the message we left. Oh, yeah." Aoba stepped to one side, letting them have a better look at his companion, now taking off her own helmet. "Let me introduce our loyal assistant, Intern Watase Tsubasa. My sister. Tsubasa, these are the guys I've been talking about all these years: the crew of the good ship _Cygnus,_ under Captain Kuramitsu Gengo and Commander Lene Kleinbeck. And this," he added, turning to look at one person in particular, "is my old partner, Junyou Dio Weinberg."

Watase Tsubasa tucked her helmet under her arm and scratched the back of her head with her free hand. "Um… hi. Aoba's told me a lot about you all. It's, ah, nice to meet you all…"

"The feeling is mutual, Watase-san," Kuramitsu said graciously, giving the girl—Dio realized with a start that Aoba's "little" sister was about his own age—a short bow. "Any of Aoba-kun's family is, of course, very welcome here. After all," he said with a wry smile, "you all did just completely turn the tide of a losing battle for us. It would be ungracious of us _not_ to welcome you."

"Even if we have _no_ idea how you're even here!" Elvira Conrad broke in, unable to contain herself any longer. "The Coupling system is only supposed to even work on elementary particles—singularity or not, the idea that that was _actually_ a time tunnel is just—and how did you even _do_ that on purpose?!"

Aoba laughed. "One thing at a time, Elvira-san. I know we've got a lot to talk about. But first…" He turned to face Dio again, the humor fading. "Yo, siscon bastard. Sorry we're late, but we wanted to avoid creating a fifth Iteration. Our first test with an unmanned drone wasn't very precise, and arriving before the events it recorded would've invoked the Temporal Observer Effect…"

Dio raised a hand. "Stop, you're making my head hurt. This is worse than the time you convinced me to go along with chasing Hina in Skyknight and Firebrand…" He trailed off, and blinked away what had to be fatigue-induced tears. "You're really here, aren't you."

"We are, Dio. And this time, we're all here to stay." There was a steady maturity in Aoba's eyes, one Dio was sure he hadn't had five years before. "Our drone test told us a lot about the current situation, and we've got some ideas to turn the tide. Elvira-san, we've got a lot to discuss—you might want to have painkiller on hand, it makes _our_ heads hurt, and we invented it. But first…"

Aoba walked toward the assembled _Cygnus_ crew, waving at Anessa and exchanging a handshake with Fromm as he went. He stopped, not to Dio's surprise, in front of Nasu Mayuka, who was visibly choking back tears. Smiling gently, he held out a hand to her.

"Hi, Mayuka-chan. Sorry I was gone so long."

Mayuka swallowed hard, and hesitantly gripped the offered hand. "It's… it's okay, Aoba-san," she whispered. "I'm just… so glad you're alive…" She bit her lip, stood still a moment longer—then threw herself at him, sobbing.

Dio quickly looked over at Hina, expecting Aoba's wife to be upset. Instead, though, all he saw was a small, sad smile, and after a moment he realized why. _They used themselves as the initial test subjects for the system. If there's any marriage that's already been tested as far as can be, it's theirs—and she's probably seen his memories of Mayuka, too. She knows as well as I do that Mayuka's not a threat—and Aoba being Aoba, he'd want to be sure she's okay._

He turned his attention then to Kleinbeck, but she only shook her head, apparently willing to let the lapse in discipline slide. Given that she was looking more than a little shell-shocked herself, he supposed it wasn't too surprising.

Something drew his attention back to the Valiancers then, and his gaze fell on Watase Tsubasa. Mostly forgotten in the emotional reunion, the young woman looked more uncomfortable than anyone, very obviously feeling out of place. She still stood by Luxon, fidgeting nervously.

 _Hard to blame her. She's the only true civilian on a ship of military personnel, and unlike Aoba or Hina she's never been to this time period before. …Why is she even here, I wonder?_

At length, Aoba pulled back from Mayuka, patted her gently on the shoulder, and turned back to the officers. "Well. I guess it's time to do some explaining? If you'll give us time to change out of these flightsuits, Elvira-san, we can take this conversation to the Captain's office." He grinned. "Hina and I will save the math for the lab, after."

* * *

Several hurried calls to higher authority later, granting their time-displaced guests provisional security clearance, a meeting was indeed called in Captain Kuramitsu's office, during which both sides brought each other up to speed on relative recent events. Much consternation was created on either end; probably the only thing about the day that _had_ gone as Dio might've expected.

"Whew," Aoba said, shaking his head, when Kuramitsu had finished outlining the highlights of the last five years of war. Like his wife and his sister, he'd traded his flightsuit for a labcoat, a look Dio still found very strange on him "I knew from what Hina told me that Bizon was the type to hold a grudge, but over seventy years? That's dedication."

"I'm wondering how in the world he survived to _get_ this far," Elvira said, rubbing her forehead. "I thought you and Doctor—er…"

"Call me Hina," Aoba's wife advised with smile. "Otherwise we both try to talk."

"Right. Hina." Elvira closed her eyes for a moment, obviously fighting off a headache. "Anyway. Didn't you two kill that guy before Dio sent you back? I've seen the footage from Bradyon's flight recorder, and he looked pretty dead to me."

Dio winced. He didn't need recordings to remember that moment; a human body being hit by a Valiancer-sized rifle was messy enough to be hard to forget.

"That was the Iteration IV Bizon," Aoba told her, stuffing his hands in labcoat pockets. He looked for all the world like a professor preparing a lecture, as bizarre as that was coming from him. "Evgeny Kedar, if my math is right, is a remnant from Iteration III."

"Iterations?" Kuramitsu asked, tilting his head. Before Aoba could reply, he raised a hand, smiling ruefully. "Is this going to give me a headache, Aoba-kun?"

"Doctor Hill will probably have it worse," Hina opined. "It's harder if you actually know some of the math."

"Simple version, then." Now Aoba assumed what was unquestionably a lecturing pose. "According to the model of the timestream we've worked out, there is only a single timeline—single, but mutable. The trick is what we call the Temporal Observer Effect: any change remains valid so long as nothing prior to it is changed, even if the original cause is an event from further down the timestream.

"Our model of the time-loops surrounding Hina boils down to four 'iterations'. Well, technically a lot more, but most of those were variations of Iteration III… Anyway." He raised one finger. "Iteration I: Hina and I develop the Coupling system on our own, without any temporal interference. Hina gets sent forward during the original test, and more or less plays out my role from the iteration we all know personally."

"You mean…" Dio frowned. "That would mean Hina was the pilot of Luxon the 'first' time around?"

"Right. Until the Battle of Alaska, when… something happened we're not actually sure of, causing the singularity that linked back to our high school days." Aoba extended a second finger. "That begins Iteration II. Bizon shows up trying to kill _Hina,_ I get caught in the crossfire, the time tunnel opens and sends her to the point Victor Ryazan adopts her, and I become Luxon's pilot." A third finger. "Events proceed as in 'our' timeline, up until Alaska, when Hina and Bizon get thrown back as in Iteration I. Begin Iteration III: Bizon comes to kill _me._ Events proceed according to that outline, give or take a few details, for… longer than we care to think about."

"Until," Hina said, picking up the thread, "Aoba and Dio succeed in Coupling with Skyknight and Firebrand." She nodded to Dio. "Seeing Aoba's memories then—that's why you chose to help him chase after me in the time-tunnel, right?"

He nodded back. "I honestly didn't believe in the time travel stuff until then," he admitted. "But when I saw that Aoba really did honestly believe everything he'd told us, and the time tunnel more or less proved it…"

Dio left it at that, not quite willing to admit why he'd acted so. That, having lost his mother to an attack he failed to stop—and almost lost his sister at the same time—he hadn't been willing to let Aoba go through the same, if he could possibly do anything about it.

Somehow, actually admitting that aloud felt like it would be conceding some kind of point to Aoba, and even after all these years that wasn't something he could do easily.

From the smile on Aoba's face, he had the feeling the crybaby-turned-physicist knew it perfectly well anyway.

If he did, though, Aoba didn't push it, instead continuing, "We did kill Bizon then, yes—but the change in timing of our fall down the time-tunnel changed our arrival point, too. We arrived _after_ Iteration III Bizon's attack, so the attack still happened—and that Bizon apparently survived his Valiancer's destruction."

"And from there, your message told us what happened." Elvira sighed. "Ugh, temporal mechanics give me a headache… Oh, thank you, Captain." She took the painkiller and glass of water Kuramitsu wordlessly set on his desk, swallowed, and turned back to their guests. "So this… Temporal Observer Effect is why you didn't show up until now?"

"Right," Hina confirmed. "We'd sent an unmanned drone ahead to get final data on calculating the trip, and we didn't want to risk creating yet another Iteration by altering the events we saw in its report. Just after the battle began was the closest we thought we could risk."

"Well, I don't think anyone on our side is going to complain about it," Kuramitsu told her, smiling. "Late or not, you did save the day—and I suspect you've got a wealth of data for Doctor Conrad, if the tricks you pulled on arrival are any indication. Having you with us is far more than anything we could've expected to gain from that old lab."

Dio nodded in agreement. Just breaking the Coupling interference Kedar had caused had been an immense help; the strange triple-Coupling even more. The implications of what might be possible _beyond_ that were staggering. And since the two inventors of the Coupling system were also veterans of using it in combat, they had a much better perspective than even Elvira.

 _But it still leaves one question. I don't even want to think about the math in their timeline model, but their "simple" version does make sense. Even so…_

"But why, Aoba?" he found himself asking, before he could stop. "You were finally back where you belonged. Back with your family, in a time before this war broke out. Why would you come back here—especially since, from what you're saying, this must be a one-way trip?"

More, come to think of it, what was his sister here for? Watase Tsubasa, Dio had noticed, had said almost nothing since arriving, letting her brother and sister-in-law do all the talking. Obviously, she wasn't anywhere near as comfortable as they were with what had been done.

Aoba took his time replying, rather than uttering something flippant the way he probably would have in the past; Dio found that as unnerving as anything else. "…There wasn't anything left for me back there, really," he said at last. "Or Hina. Dio, from our point of view it's been eight years since we left this time; things have changed. My mother died before we perfected the Coupling system, and honestly, I had closer ties to people in this time than I ever did to those in my own. And Hina…"

"Technically, I'm like Bizon," Hina said quietly. "I'm from a no-longer-valid iteration of the timeline. My parents were still alive—but they had another Hina, one growing up normally. After I stopped looping, Aoba's family was the only one I really had. When his mother died, and Tsubasa got so involved in the Coupling project…"

"It was easier this way, I guess." Tsubasa's contribution was quiet, hesitant; but Dio got the impression she at least wanted to make clear she was there by her own decision. "I didn't have anybody left, and Aoba said he had friends here… And honestly, can you get a bigger career boost than being part of something like this?"

Dio grimaced, but didn't pursue the point any further. _This wasn't what I had in mind, when I pushed them back into the time-tunnel. I thought they'd earned their peace, away from this war… but it's their decision to make. Anyway, what would I have done, if I'd lost the rest of my family, and had a chance to go somewhere I knew I had friends?_

It wasn't like he was _upset_ that Aoba was back, after all. He had no intention of admitting it, but he didn't really think it was a bad thing, at all.

Kuramitsu gazed at them silently for a time, seeming to weigh the matter himself. As usual, his thoughts were difficult to gauge, but in the end, he shrugged, leaned back in his chair, and smiled. "I don't know that I'd have made the same choice myself, Doctors, but speaking as someone who's getting very tired of this war, I'm glad you're here. Any assistance you give us, on the battlefield or in the lab, will be much appreciated. Ah… that is, if you're intending to stay with the military?"

Aoba and Hina exchanged a quick glance. "I think some kind of civilian contractor status might be best, if we can swing it," the former said. "Not that I really minded being a soldier or anything, but we're going to be doing at least as much pure science as fighting, maybe more, so the distinction could get kinda blurry."

"I suspect something can be worked out. In the meantime, once again, welcome back, Aoba-kun. I'd suggest you get some rest, for the time being." Kuramitsu was still smiling, but his eyes had noticeably sobered. "It's hard to believe Kedar is doing all this out of such a petty grudge, but whatever his reasons, I doubt he'll give up now. We're all going to be busy, when his forces have regrouped."

* * *

As glad as he was to have Aoba around again—not that he was inclined to admit it, even under the most brutal torture—Dio found himself needing an escape after the discussion moved to _Cygnus'_ onboard lab. Pure Coupling theory had always been hard on his brain, however good he'd proven at practical application; the concepts and math being thrown around now were completely over his head.

 _Aoba went and became a scientist,_ he thought, making his way to the hangar. _That's… utterly mind-boggling. When did he get so smart?_

Probably, Dio mused, when he found his new partner. It was obvious Hina was good for Aoba on more levels than just emotional; even their Emphatier waveforms were a perfect match, even more so than Dio's had been.

Which, he had to admit, if only to himself, was part of why he was feeling so lost. Aoba was finally back—but he wasn't really Dio's partner anymore. Three years more had passed for the scientist than the soldier, and under very different conditions. Clearly, when they did enter the battlefield once again, even with the experimental three-way Coupling, Hina would be Aoba's main partner now.

Dio could live with that. He'd spent five years without his partner—friend, if he were forced to be completely truthful—around at all; this was just one more adjustment. It only made it a little harder.

Reaching the hangar, he was surprised out of his contemplation by the discovery that he wasn't the only non-mechanic who'd dropped by. Standing on the catwalk in front of Luxon NX, Watase Tsubasa leaned on the railing, looking completely lost in thought.

Curious, Dio cautiously approached Aoba's time-lost sister. "Miss Watase?" he said. "I'd have thought you'd be in the lab, with Aoba and Hina."

She jerked, startled. "Eh?! Oh… Weinberg-san, right?" Tsubasa shrugged, turning her attention back to her brother's Valiancer. "I'm still an intern; the kind of math they were getting into with Doctor Conrad was making my head hurt. When they're ready for more experiments, they'll call me in."

"I'm glad it's not just me." Turning to lean against the railing himself, a discrete couple of meters away, Dio ruefully shook his head. "Back when _I_ last knew Aoba, he wouldn't have understood any of this, either. Most of the breakthroughs we made with him were because he was too ignorant to know what was impossible. Hearing him talk like Doctor Conrad is unnerving."

"You're telling me? I grew up with the guy." Tsubasa snorted. "One day he's the same old, always late for school, barely keeping his grades up brother of mine, who probably never talked to a girl outside the family in his life. Then a giant robot attacks out of nowhere, Aoba comes home with a girl, and he hits the books like he's trying to be the next Hawking. It was so weird I actually thought time travel made it make _sense!"_

Dio found himself nodding. "Aoba's like that. He's always doing crazy things—and it just makes it harder to take when he's right about something. He was only on _Cygnus_ a few weeks, but he gave us plenty of headaches doing the impossible." Looking over at Luxon NX, he couldn't help but remember the very first impossibility: Aoba's appearance out of thin air in the original Luxon's cockpit.

 _We should've known something weird was going on from the very start,_ he thought. _Lack of records and his crazy story could've meant he was a spy—a really_ bad _spy—but there really wasn't any logical way he could've gotten into the cockpit. Not when it was covered in rubble._

Off to his right, Tsubasa sighed. "So… this really is seventy years in the future, huh? Even after everything, it's hard to believe Aoba really was telling the truth about his crazy time travel adventure."

"It wasn't any easier for us to believe he was from the past," Dio told her, smiling reluctantly at the memory. "Of course, I always thought he was too stupid to be a spy, but honestly it seemed more likely he'd taken one too many hits to the head—especially since Doctor Conrad was so sure time travel on anything but particle-level was impossible."

"Aoba _always_ seemed like an idiot back then," she said, rolling her eyes. "If it weren't for me, he never would've gotten to school on time. Time travel? Ending up as some kind of hotshot ace pilot in the future? If he hadn't had a giant robot, I never would've believed it when he finally got around to telling me. …Actually, I never really _did_ believe it, until we accidentally sent Hina to the future in that first experiment." Tsubasa shot him a sidelong glance, one eyebrow raised. "So? How he'd convince _you_ guys he wasn't crazy? That kind of crazy, I mean?"

Dio surprised himself with a chuckle. Watase Tsubasa, he was discovering, was very easy to talk to—their shared source of exasperation was probably a help. "Well, it was pretty obvious _he_ believed it, if only because of how many times he almost got himself killed trying to get through to Hina. It wasn't until we did a Coupling with Skyknight and Firebrand that I really started to believe it myself, though."

He still remembered that glimpse into Aoba's memories. Brief though it had been, it had been vivid, and far too "real" for him to doubt any longer that his irreverent partner wasn't from the present world.

"Of course," he continued, "it wasn't that easy for everyone else. I think Doctor Conrad wrote it off as a hallucination caused by the unstable Coupling System the prototypes had. At least, until the Battle of Alaska happened." Dio shook his head, chuckling at the memory—one that he could finally find some humor in, now that he knew he hadn't made a colossal mistake that day. "Having a singularity open in the sky was kind of hard to ignore."

"I bet." Tsubasa shivered. "Just so you know? Those _really_ aren't fun to actually go through, Weinberg-san. I didn't like reality taking a lunch break when Hina and Bizon first showed up with giant robots in the middle of Tokyo. It's worse when you know the math."

"Doctor Conrad's reaction a couple hours ago told me that much already, Miss Watase." Dio hesitated. "And call me Dio. If that crybaby does, his saner sister might as well, too. …Just don't call me a siscon."

Tsubasa blinked, then slowly grinned. "Hey, anybody who realizes I'm the real smart one in the family gets to call me Tsubasa, Dio." She stuck out a hand. "I dunno what's going to happen next, but you can bet my brother is going to come up with another harebrained scheme soon. It's up to us to try and keep his head out of the clouds, right?"

Finding himself smiling back, Dio shook the offered hand. "If I know Aoba, we'll just be dragged along anyway—but at least we can watch out for the speed bumps, Tsubasa. He was bad enough at getting distracted in combat before; I can't imagine becoming a scientist has made him any better at focusing."

"It hasn't, believe me. He's better at being on time these days, but once something gets his attention—"

They were interrupted by a chime from the hangar's PA speakers. _"Yo, Dio, Tsubasa,"_ Aoba's voice called out. _"Could you two both come to the lab? I had an idea."_

Dio closed his eyes, counted to ten, and tried to prepare himself for a headache, before quickly crossing to the closest intercom panel. "Aoba. Do I even want to know what you have in mind this time?"

" _Easier to show you, Dio. Let's just say Hina, Elvira, and I were looking over Tsubasa's Emphatier_ _waveforms, and your latest results—ah, it's complicated. Just get to the lab, will ya?"_

" _Bring some painkiller,"_ Elvira's voice cut in, sounding resigned. _"Trust me, you'll need it when the tests are done."_

 _Tsubasa's been tested with the Coupling System? And…_ my _last recorded waveforms?_ Dio shot a glance at Tsubasa, but she only shrugged. _Aoba… what_ are _you up to this time?_

"We'll be right there," he said cautiously. "Though I'm getting a very bad feeling about this." Shutting off the intercom before Aoba could reply, he looked back at Tsubasa. "Any idea what your brother and sister-in-law are up to now?"

"Beats me." Joining him as he headed back out of the hangar, Tsubasa frowned. "I mean, sure, they got a full readout on my Emphatier waveforms not too long before the jump, but I figured that was just for a control sample. No idea what Aoba's thinking of now." The look she gave him now was a wary one. "This _is_ the guy who invented time travel, though. I think we're gonna need that painkiller."

Sighing, Dio could do naught but nod in agreement. _Just be glad it's not Doctor Hahn,_ he told himself. _Aoba's saner than that. Well… more ethical, anyway._

 _The day I think Aoba is "sane" will be the day I know I've lost_ my _mind._

* * *

 **And Now, A Word From The Author**

The better part of two years is, I admit, rather longer than I meant to take with this—and it's not even quite finished, as is probably obvious. Deepest apologies; my time has not been my own as much as I'd prefer, and honestly writer's block was somewhat involved.

Which is why the chapter cuts off here: the remainder of the plot would heavily involve combat, and Valiancer combat is something I have difficulty wrapping my mind around—too little technical detail given in canon. Someday perhaps I will work in _Gundam,_ which has if anything an excess of detail…

In the meantime, at least Chapter 1's cliffhanger is resolved, yes? I know this chapter is far less interesting than the first, but I hope it provides at least some closure. I do intend to eventually provide a proper conclusion to this tale, but regrettably I can make no promises as to when.

However, with this off my mind for the time being, hopefully I can get some work done on projects I have more concrete plans for. I shall see you around, dear readers.


End file.
